1. Field of the Invention
The present invention generally relates to a fluid monitoring sensor and, more particularly, to a new and improved sensor used in analyzing blood glucose or other analytes contained therein that is configured so that as the sensor is being ejected from a cavity of a sensor pack loaded into a dispensing instrument, a shard of the sensor pack material will not be severed that could otherwise interfere with the proper operation of the dispensing instrument.
2. Description of the Prior Art
People suffering from various forms of diabetes routinely need to test their blood to determine the level of blood glucose. The results of such tests can be used to determine what, if any, insulin or other medication needs to be administered. In one type of blood glucose testing system, sensors are used to test a sample of blood.
Such a sensor may have a generally flat, rectangular shape and is formed from two pieces of mated plastic, a base portion and a lid portion. The sensor has a front or testing end and a rear end. The sensor contains biosensing or reagent material that will react with blood glucose. The testing end of the sensor is adapted to be placed into the fluid being tested, for example, blood that has accumulated on a person's finger after the finger has been pricked. A sufficient amount of fluid to be tested is drawn into a capillary channel that extends between the mated pieces of the sensor from the testing end to the reagent material by capillary action. The fluid then chemically reacts with the reagent material in the sensor with the result that an electrical signal indicative of the blood glucose level in the blood being tested is supplied to contacts located on the exterior of the sensor.
In order to couple the electrical signals produced at the sensor contacts to monitoring equipment, the sensors need to be inserted into sensor holders prior to the sensor testing end being placed into the fluid being tested. The holders have corresponding mating contacts that become coupled to the contacts on the sensor when the sensor is inserted into the holder. Consequently, the holders act as an interface between the sensor and monitoring equipment that accumulates and/or analyzes the test results.
Prior to being used, the sensors need to be maintained at an appropriate humidity level so as to insure the integrity of the reagent materials in the sensor. Sensors can be packaged individually in tear-away packages so that they can be maintained at the proper humidity level. For instance, blister type packaging methods could be used. In this connection, the packages can include desiccant material to maintain the proper humidity or desiccate level in the package. In order for a person to use an individual sensor for testing blood glucose, the package must be opened by tearing the seal. Alternatively, some packages require the user to exert force against one side of the package resulting in the sensor bursting or rupturing the foil on the other side. As can be appreciated, the opening of these packages can be difficult. Moreover, once the package is opened, the user needs to be sure that the sensor is not damaged or contaminated as it is being placed into the sensor holder and used to test the blood sample.
Sensor dispensing instruments have been developed for dispensing individual ones of the sensors to a sensing position from within a sensor pack loaded into the sensor dispensing instrument. One such type of sensor pack includes a generally circular shaped base portion in which is formed sensor retaining cavities or depressions. Each of the sensor retaining cavities is adapted to receive one of the sensors and is in fluid communication with a corresponding desiccant cavity in which is disposed desiccant material. The desiccant material is placed in the cavity to insure that the corresponding sensor cavity is maintained at an appropriate humidity or desiccate level so that the reagent material in the sensors will not be adversely affected prior to the sensors being used. A foil is heat sealed onto the base portion about the entire outer peripheral edge of the base portion and about the entire perimeter of each set of sensor retaining and desciccant cavities to seal the sensor retaining cavities and the desiccant cavities. As a result, the individual sensors are maintained in a desiccated state and in addition are isolated from each other such that the opening of one sensor cavity will not adversely affect the desiccated state of any other sensor cavity.
The circular type sensor pack can be loaded in a sensor dispensing instrument that has a feeding mechanism. When the feeding mechanism is actuated or moved forward toward a testing end of the instrument, one of the sensors in the sensor pack is ejected from the sensor pack and placed into a sensing position. In this regard, a driver on which is mounted a knife blade moves toward one of the sensor cavities in the sensor pack that is positioned in alignment with the knife blade as the feeding mechanism is moved forward. The knife blade pierces the foil covering that sensor cavity and engages the rear end of the sensor disposed in that cavity. As the driver continues to be pushed forward, the knife blade further severs the foil covering the sensor cavity and forces or ejects the sensor out from the sensor cavity causing a front biased edge of the sensor to burst through the outer foil covering the sensor cavity. As the sensor is being forced out of the sensor cavity, the sensor travels along a sloped support wall at the base of the sensor cavity so that as the sensor is advanced by the knife blade, the sensor will avoid being forced into the heat seal that affixes the foil to the base portion of the sensor pack. The force required to drive the sensor through the foil is in part determined by the specific geometry of the front end of the sensor.
The sensor is guided into its testing position with the testing end of the sensor projecting out from the testing end of the instrument. When in the testing position, contacts in the instrument become mated with corresponding contacts on the sensor. The sensor dispensing instrument may include a microprocessor or other data processing circuitry that is electrically coupled to the instrument contacts so that data obtained from the sensor when it is inserted into blood being tested can be processed. The processed data then can be displayed on a screen of the instrument or stored for use in other analyzing equipment.
After the fluid has been analyzed, the feed mechanism can be used to eject the used sensor from the testing end of the dispensing instrument. Thereafater, the feed mechanism is retracted to a standby position resulting in the sensor pack being rotated so that another sensor cavity is in alignment with the knife blade on the driver mechanism and another sequence can be initiated to eject another one of the sensors from the sensor pack.
As previously indicated, the sensor is from mated plastic lid and base portions between which is sandwiched the reagent material. The testing end profile of both the lid and base portions of the sensor need to be configured such that the sensor will burst with a minimum of force through the thin foil that overlies the sensor cavities of the sensor pack. However, the testing end edges of the lid and base portions may result in the tearing of a shard of foil (a little piece of foil that separates from the foil overlying the sensor cavities) as the sensor is being ejected through the foil from a sensor cavity. The severed shard of foil either may block the capillary channel inhibiting the fluid to be tested from flowing into the sensor or may short circuit the instrument or sensor contacts thereby rendering the instrument inoperative.
The formation of such a shard of foil tends to be caused by the configuration and spatial relationship of the mated plastic pieces (i.e., the lid and base) at the testing end of the sensor. When the lid and base are not sufficiently offset longitudinally (i.e., in the direction from the rear end to the front end of the sensor) with respect to each other, the base and lid creates two cutting edges so that the foil tends to be cut by a scissoring like action rather than being severed. This scissoring action tends to result in a small piece or shard of the foil be severed from the foil overlying the sensor cavity. The angle of the lid and/or base with respect to the transverse axis of the sensor also can contribute to the formation of a shard of foil. For example, a shard of foil may be torn from the foil when the testing ends of the lid and base are biased at a continuous (usually obtuse angle) with respect to the transverse axis of the sensor. In view of the fact that any shard of foil that becomes detached from the foil overlying the sensor cavities can adversely affect the operation of the sensor instrument, it would be advantageous to insure that no shard of foil will become detached during the ejection of the sensor from the sensor cavity.